Telephone transmitter



Dec. 20, 1938. o. SOLDAN ET AL 2,14%859 TELEPHONE TRANSMITTER Filed Dec. 16, 1937 Patented Dec. 20,

. UNITED STATES) PATENT OFFICE 2,l4ll,859

TELEPHONE 'rn NsmrTEn; Otto Soldan, Falkensee, near Berlin, and Hans I I Panzerbieter and Bernhard Jiirgensen, Berlin- Siemensstadt, Germany, assignors to Siemens & Halske Aktlengesellschaft, Wernerwerk Siemensstadt, near Berlin, Germany Application December 16, 1937, Serial No. 180,152

' In Germany December 14,1936

8 Claims. (01. 179-122 The subject of the invention is a cross current microphone. construction for improving the operation of such a microphone. g

In cross current microphones in which the path of the current is parallel to the diaphragm it is of considerable importance that the granules controlled by the diaphragm should in all positions be in contact with the diaphragm and that in all positions the electrodes of the carbon granule chamber should be covered by granules.

In the previously known arrangements these requirements were only partially met. It is, for example, known to provide cross current microphones with a plurality of granule chambers extending parallel to one another and to enclose these with a fluted diaphragm. With this arrangement a reinforced diaphragm was produced and the area over which thecarbon granules and ing body disposed between the'electrodes forms.

a conical granule chamber. The path of the current between the outer and inner electrodes thus has a part which is inclined to the direction of the gravitational force operating on the granules in every positionin which the microphone may be situated. Thus even in the most unfavorable position of the microphone the granules of carbon, which are subject to the action of gravity, always bear against the diaphragm with a certain pressure, this being of considerable importance in the case of cross current microphones from the point of View of uni? form control, independent of position,- of the granules disposed between the electrodes. The shape of the diaphragm and of the base of the chamber produces a complete freedom from interruption since thecarbon granules cannot depart from the electrodes nor can the electrodes emerge completely from the granule region in any position of the microphone. According to the invention the granule chamber thus con structed is preferably divided by felt layers into radially disposed current paths of equal cross section as has already been proposed for other microphones whereby non-linear distortion is avoided. For this purpose the invention provides for a correspondingly shaped felt layer to be fixed on the inner surface of the diaphragm. Through fixing the felt layer to the diaphragm the felt participates in the controlling of the granules, the felt fibres preventing the granules The invention is directed to the from pa'cking. A particularly desirable arrangement is produced by the invention in that the felt is fixed by means of the insulating matter which insulates the diaphragm from the. carbon granules whereby on the one hand the felt layer is securely attached particularly at its margins and on the other hand the felt, exerts a much smaller damping effect on the diaphragm than would be the case if it were fixed to the diaphragm in the usual way bysticking means which would soak into the felt and impart to this a certain rigidness which would have a damping eifect- Preferably the base of the insulating member forming the granule chamber between theelectrodes is provided with depressions serving as supply chambers for the carbon granules from which the granules can flow to the electrodes in the appropriate position of the microphone.

The carbon granule chamber can be made either concave or convex. The latter has the advantage that the diaphragm can be brought closer to the source of sound i. e., to the mouth of the user and that a large air space in front of the diaphragm is avoided, this in particular cases having an undesirable effect on the frequency response of the microphone.

With the concave carbon granule chamber a large space in front of the diaphragm can be avoided by inserting a member between the mouthpiece and the diaphragm which is adapted on the one'side to the shape of the diaphragm and on the other side to the shapeof the mouthpiece.

A further improvement of thearrangement according to the invention is produced by making the insulating member disposed between the electrodes and constituting the base of the chamber of ceramic material. The ceramic material possesses a larger heat conductivity than the usual insulating compressed material or. hard rubber and thus the properties of the microphone are considerably improved. This, is particularly important in cross current microphones which have a high direct current consumption. Instead" of the ceramic material lacquered metal can be usedythis already having been proposed per se. An embodimentof the invention is described and illustrated in the following:

Figure 1 of the drawing represents a cross section through the microphone according to the invention.

Figure 2 is a further embodiment of the cross current microphones according to the invention and Figure 3 is an underneath viewof the diaphragm with the felt coating. I

As may be seen from Figure 1 the microphone consists of a housing I which is closed in the known way by the cover plate 2 provided with apertures which is fixed to the housing I bya material. The insulating member 3 extends between an outer annular-electrode I arid an inner central electrode 8. The electrode 8 abuts under spring action against-the housing I by means of a spring 9 which is also connected to the current lead III which is insulated from the housing I. The annular electrode 1 is in conductive connection with the housing I. and the insulating member 6. combine to form a carbon granule chamber of conical form which may be concave as shown in Figure 1 or convex as shown in Figure 2. The granule chamber 4 is divided intoradial current paths of equal cross section by means of a felt layer fixed to the diaphragm 5. the form of this layer being represented in Figure 3. The felt layer ll abuts against the insulating body 6. In order to securely fix the felt layer I I to the diaphragm 5, it is attached by means of the insulating layer of lacquer on the inside of the diaphragm. This may be shown byapplying the felt before the last layer of lacquer has dried. The lacquer which causes good adhesion particularly around the margins of the felt layer ll does not permeate the layer itself so that this is not unnecessarily stiffened and thereby does not give rise to'too great a damping of the diaphragm 5. The application of the felt layer II to the diaphragm 5 has also the advantage that the felt layer can participate in the controlling of the granules and the minute hairs prevent the granules becoming packed when the diaphragm'is stressed unduly. The conical form of the granule chamber 4 ensures that in the horizontal position of the microphone the granules under the influence of gravity have a certain pressure operating on the diaphragm thereby eificiently maintaining the mechanical ,contact' between them and the diaphragm even in this most disadvantageous position thus enabling an emcient control of the granules. Moreover, the electrodes 1 and 8 are always covered with granules in every position of the microphone.

Conveniently the central electrode 8 is given a conical form to increase the independence of the microphone on the position in which it is disposed. In this casethe portion of the diaphragm facing this electrode is shaped correspondingly. As may be seen from Figures 1 and 2 the insulating member 6 possesses depressions I! which serve as supply chambers for the carbon granules.

The electrodes I can be-burnt into the insulating member of ceramic material.

In order to reduce the air space disposed in front of the diaphragm 5 in the case of the concave arrangement according to Figure l and thereby to produce a better frequency response for the microphone, a member ll can be arranged substantially to fill this air space, this being indicated in dotted lines in Figure 1.

What is claimed is:

1. In a microphone, a diaphragm, a rigid insulating member of similar shape and diameter, a

pair of electrodes fixed thereon so that one electrode, concentric to the other electrode, is at the outer edge of said rigid member, a conical carbon chamber formed by said elements, a non-rigid in- The diaphragm I sulating memberin said chamber with sections cut away so that channels for carbon granules are formed parallel to the diaphragm extendin radially to said outer electrode, said rigid mem-- ber having concentric channels formed on the inner surface by ridges thereon so as to be ad jacent to said. channels of said non-rigid member.

'2. In a microphone, a diaphragm, a rigid insulating member of similar shape and diameter, carbon granules, a pair of electrodes fixed thereon so that one electrode, concentric to the other electrode, is at the outer edge of said member, a

conical carbon chamber formed by said elements for said granules, a non-rigid insulating member in said chamber attached to said diaphragm having sections cutaway so that channels are formed wherein current pathsthrough carbon granules" may extend radially parallel to the diaphragm to said outer electrode and be controlled by direct pressure of the diaphragm at any of the points along said channels.

3. A microphone as claimed in claim 2, wherein said carbon granules comprise the only means therein other than said'fixed electrodes for transmitting current.

. 4. A microphone as claimed in claim 1, wherein said rigid insulating member may be of ceramic material formed around said rigid electrode at I its outer edge.

5. In a microphone, a diaphragm and an insulating member forming a carbon granule chamber, electrodes secured to said member, concentric grooves in said members forming pockets for the carbon granules, and an insulating washer secured to said'diaphragm and having radial grooves therein also forming pockets for the carbon granules.

6. In a radial flow microphone wherein current flows from a center electrode to a ring electrode, a diaphragm and an insulating member forming the front and back walls respectively of a coneshaped carbon granule chamber, a series of ridges in said insulating member preventing free cross flow of the carbon granules in said chamber, and an insulating washer completely filling the space between the ridges and the diaphragm at points, and cut away at other points to provide radial grooves permitting cross flow of the carbon granules in said chamber. I

7. In a microphone, a pair of fixed electrodes, a diaphragm, a carbon chamber, an insulating washer in the chamber cut away to provide a plurality of current paths between the electrodes, said diaphragm acting on the carbon granules in all of said paths to vary the resistance thereof in all paths, the wall of said chamber opposite said diaphragm having ridges therein forming channels each 01' which runs in a different direction than all of said first paths.

8. In a microphone, a diaphragm, a carbon granule chamber having a rear insulating wall and' a front wall formed by the diaphragm, a center electrode and a ring electrode in said chamber, said diaphragm when vibrated varying the resistance of the granules in said chamber, a plurality of circular grooves in the wall of the chamber, and an insulator in the chamber havv 

